- medical school, University of Pennsylvania
- practiced medicine 1844-1847
- teacher, University of Pennsylvania
- Surgeon, US Army (Civil War)
- Professor, at University of Pennsylvania and Swarthmore College
- discovered Trichina larvae in pigs
- Biologist, Educator, Paleontologist
- father of American vertebrate paleontology
- 100 new species of intestinal parasites.
- Leidy quote from Warren 1998 (citation)- "How can life be tiresome so long as there is still a new rhizopod undescribed?"